1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier, a printer, or a facsimile machine, and more particularly to a technology for preventing degradation of toner image quality therein.
2. Description of Related Art
JP-A-H8-314253 discloses and proposes an image forming apparatus provided with: toner consumption means that forcibly consumes toner accommodated in a developer container of a developing device; and control means that controls the toner consumption means and toner supply means in such a way that the toner accommodated in the developer container is forcibly consumed and toner is forcibly supplied thereto when developer (including toner and carrier) has been agitated for a predetermined period or longer without any consumption of the toner accommodated in the developer container.
According to the image forming apparatus disclosed in JP-A-H8-314253, since the toner accommodated in the developer container is forcibly consumed and toner is forcibly supplied thereto when the developer (including toner and carrier) has been agitated for a predetermined period or longer, it is possible to prevent degradation of the toner resulting from friction between the toner and the carrier agitated in the developer container.
However, the image forming apparatus disclosed in JP-A-H8-314253 is so structured that the period for which the developer (including toner and carrier) has been agitated without any consumption of the toner accommodated in the developer container is not stored in memory means. Hence, if the power to the apparatus is turned off before the period for which the developer has been agitated without any consumption of toner accommodated in the developer container reaches the predetermined period and then the power to the apparatus is turned back on, the period for which developer has been agitated without any consumption of the toner accommodated in the developer container starts to be counted from scratch. Thus, the length of time required for that period to be found to have reached the predetermined period may become longer than it should be. Hence, it may occur that, although the period for which the developer has been agitated without any consumption of the toner accommodated in the developer container is not yet found to have reached the predetermined period, in fact a toner image is formed on paper with degraded toner. This degrades the quality of the toner image formed on the paper.
In addition, JP-A-H8-314253 does not describe in detail the counting of the period for which the developer has been agitated without any consumption of the toner accommodated in the developer container in a case where development accompanying printing (that is, consumption of toner) takes place before that period has reached the predetermined period.
In view of the above described problems, an object of the present invention is to provide an image forming apparatus that is free from the loss of the count result of the period for which toner has been agitated without any discharge of toner out of a development unit, even when the power to the apparatus is once turned off, and that thereby prevents degradation of toner image quality.